1. Field of the Invention
The invention relates to a polyaxial bone anchoring device that facilitates pivoting of a bone anchoring element at high angles relative to a receiving part. The device includes the bone anchoring element having a shank for anchoring in a bone or a vertebra and a head, and the receiving part for receiving a rod to be connected to the bone anchoring element. An insert piece is rotatably mounted to the receiving part. The insert piece has a seat for the head of the bone anchoring element and is configured to permit the bone anchoring element to pivot at a larger angle at a first location than at a second location relative to the receiving part. The insert piece is supported in the receiving part by a flat surface portion on the receiving part that engages a corresponding flat surface portion of the insert piece.
2. Description of Related Art
A polyaxial bone anchoring device with an enlarged pivot angle is described in U.S. Pat. No. 6,736,820. This bone anchoring device includes a bone screw and a receiving part with a seat for the head of the bone screw. The screw member can be pivoted to at least one side by an enlarged angle, because the edge bounding the free end of the receiving part is of asymmetric construction. In a modified embodiment, an insert piece is provided, which has a spherical bottom as a seat for the head of the screw member.
U.S. 2005/0154391 A1 describes a bone anchor assembly including a bone anchor having a distal shaft configured to engage bone and a proximal member. The proximal member may have a first section and a second section coupled to at least a portion of the bone anchor. The second section may be movably connected to the first section to facilitate relative rotation of the first section and the second section.
U.S. 2007/0118123 A1 describes a polyaxial bone anchor with increased angulation. The polyaxial bone anchor has a locking element shaped and configured to allow an anchoring member, e. g. a screw or a hook, to polyaxially rotate at large angles about a central axis of the bone anchor before compression locking the anchoring member within an anchor head.